1. Field of the Invention
The present invention relates to semiconductor device fabrication. More particularly, the present invention relates to a mask pattern for fabrication of a semiconductor device with a fine pattern above the wavelength limit of lithography, a method of forming the same, and a method of fabricating a finely patterned semiconductor device using the mask pattern as an etching mask.
2. Description of the Related Art
In a conventional semiconductor device fabrication patterning process, a photoresist pattern is formed on a predetermined film, for example, a silicon film, a dielectric film, or a conductive film. Then the predetermined film is etched by using the photoresist pattern as an etching mask to form a desired pattern.
With the trend towards increasing integration of semiconductor devices, the industry has established certain design criteria for smaller critical dimension (CD) and a new lithography technology for forming fine patterns including contact holes having a smaller opening size or spaces having a smaller width.
In a conventional lithography technology for forming smaller-sized contact holes, a short-wavelength exposure tool, like in E-beam lithography, or a half-tone phase shift mask is used. The short-wavelength exposure tool based lithography has many difficulties because it is material-dependent and uneconomical. The half-tone phase shift mask based lithography has limitations on mask formation technology and resolution, and thus, it is very difficult to form contact holes which are less than 150 nm in size.
Hitherto, various technologies for satisfying the need of a smaller feature size have been suggested.
For example, Japanese Patent Laid-Open Publication No. 1989-307228 discloses a technology of forming a fine resist pattern by exposure and development of a resist film and then thermally treating the resist pattern so that the profile shape of the resist pattern is changed. According to this technology, however, a resist flow rate is different in the upper area from the middle area of the resist pattern. In particular, when the CD of the resist pattern to be reduced by thermal flow is 100 nm or more, the profile of the resist pattern is transformed by rapid flow characteristics of the resist film. As a result, a bowing profile in which a swelling phenomenon takes place near the middle area. Therefore, this technology has a limitation in adjusting the flow rate of the resist pattern, which makes it difficult to reduce the CD of the resist pattern while maintaining a vertical profile shape.
Japanese Patent Laid-Open Publication No. 1995-45510 discloses a method of forming a fine pattern, which includes: forming a resist pattern and coating a resin immiscible with a resist on the entire or partial surface of the resist pattern, followed by thermal treatment to flow the resist. According to this method, excessive flow can be prevented since the thermal flow of the resist is generated after the resin coating. However, polyvinylalcohol used as the resin has a high viscosity and is water-insoluble, and thus, it is difficult to completely remove the resin by rinsing with deionized water.
Japanese Patent Laid-Open Publication No. 2001-228616 discloses a method of decreasing both the hole diameter and the isolation width of a resist pattern by increasing the thickness of the resist pattern. According to this technology, the resist pattern that can serve as an acid donor is coated with a framing material that can serve as an acid acceptor for crosslinkage with the acid. When the acid is transferred from the resist pattern to a layer made of the framing material by heating, a crosslinked layer is formed as a layer covering the resist pattern at an interface between the resist pattern and the framing material layer. However, a chemical crosslinking reaction may also occur at an unwanted position, thereby causing pattern defects.
Japanese Patent Laid-Open Publication No. 2003-202679 discloses a method of forming fine patterns using a coating agent. The coating agent is coated on a substrate having photoresist patterns to decrease spacing between the photoresist patterns by the thermal shrinkage effect of the coating agent. However, since the amount of thermal shrinkage in the coating agent depends on the temperature profile of the substrate, it is difficult to form uniform resist patterns on the entire substrate surface.
As described above, in CD reduction technologies that have been suggested hitherto, crosslinkage takes place between a photoresist and an organic polymer and a thermal treatment for resist flow. However, these methods have a disadvantage in that a resist pattern has a low resistance to dry etching. With respect to a CD reduction technology based on a crosslinkage between a photoresist and an organic polymer, a crosslinked layer coated on the surface of a resist pattern is mainly made of a hydrocarbon compound, which has a low dry etching resistance, relative to a photoresist material. On the other hand, with respect to a CD reduction technology based on a thermal treatment for resist flow, the thickness of a resist pattern made of a photoresist material decreases during thermal flow of the photoresist material, thereby lowering a resistance to dry etching.
A way to increase dry etching resistance of a resist pattern is to use a silicon-containing material. U.S. Pat. No. 6,110,637 discloses a method of forming a fine pattern by crosslinkage between a photoresist with a carboxylic acid anhydride functional group and an aminosiloxane oligomer. However, this method has disadvantages in that a specific photoresist material crosslinkable with aminosiloxane is needed and, separately, an organic solvent is required for removing the unreacted silicon-containing material that remained after the crosslinkage.
U.S. Patent Application Laid-Open Publication No. 2004/0009436 A1 discloses a method of coating a silicon-containing material layer on a resist pattern by crosslinking a silicon-containing water-soluble polymer with the resist pattern. However, the silicon content is restricted, and thus, it is difficult to obtain sufficient resistance to dry etching.